From what I remember the 24 months is only relevant to the “builder / main contractor” who I thought had to be a signed up member of the scheme, it doesn’t apply to anyone who is a subcontractor to that builder unless there is some kind of flow down in a contract.
For property refurbs, office fit outs etc I am usually on the hook for 12 months, although customers have agreed to as little as 3 months when we haven’t done anything massively structural.
I guess it all comes down to what is in your contract as others have said.
Paul